1. Field of Invention
The process in accordance with the present invention is applicable generally to manganiferous oxide ores that contain a major amount of manganese in the tetravalent state and iron and a minor amount of nonferrous metals including at least one of the metals nickel, cobalt or copper. It will be described herein, however, in conjunction with deep sea nodules. The nodular deposits are found in large quantities on the ocean floor and are a potential source of metals. The physical and chemical nature of these deposits vary depending on their location. Typical deposits can contain, for example, up to about 2% nickel, up to about 2% copper, up to about 1% cobalt, up to about 25% iron and up to about 40% manganese. Since the components are tied in intimate and complex association they are not amenable to separation by conventional beneficiation procedures. For the same reason extraction of the valuable metals is difficult.
2. Prior Art
Numerous methods have been proposed for extracting metal values from sea nodules. Among them are processes which use sulfur dioxide, to extract nickel, copper and cobalt in neutral or acidic media. U.S. Pat. No. 3,169,856, for example, uses sulfur dioxide or nitrogen dioxide to preferentially dissolve the values in the manganese phase leaving the iron phase in the residue for subsequent treatment. Similarly, German Pat. No. 2,150,785 leaches the ores, preferably in the presence of added MnSO.sub.4, with SO.sub.2 to dissolve preferentially the manganese phase leaving the iron phase in the residue for further acid treatment. In U.S. Pat. No. 3,810,827, nodules are treated with SO.sub.2 in a fluid bed in the absence of oxygen to sulfate preferentially the manganese content of the nodules. Leaching the sulfated nodules dissolves manganese leaving the remaining nonferrous values in the residue for dissolution in a subsequent treatment. In each of these processes, most of the manganese content of the nodules is dissolved in a weakly acidic liquor containing at least a portion of the copper, nickel, or cobalt present in the nodules. Separation and recovery of the valuable nonferrous metals and manganese from these solutions may be complex and expensive.
Other processes are known to utilize leaching in ammoniacal solutions to extract the valuable nonferrous metals leaving manganese and iron in the residue. Among these are processes such as U.S. Pat. No. 3,471,285 which involve high temperature selective reduction of the nodules prior to leaching in the ammoniacal medium. These processes are becoming less attractive because of the large energy requirement to dry and heat the nodules. Another process, U.S. Pat. No. 3,728,105, leaches the nodules in ammoniacal media at temperatures between 100.degree. and 300.degree. C. under atmospheres containing H.sub.2 and/or CO at 300 to 1000 psig total pressure to reduce the Mn and selectively extract the Cu, Ni, and Co. The cost of pressure vessels to withstand such high temperatures and pressures in addition to the large energy requirement for heating a slurry makes this process unattractive.
It is an object of the present invention to provide an improved method for treating manganese oxide ores, especially manganiferous sea nodules, in which copper, nickel and cobalt are selectively separated from manganese. Another object is to provide a method in which neither thermal pretreatment nor drying of the ore is required. A further object is to provide a hydrometallurigical method in which leaching of the ore is carried out under essentially atmospheric pressures. It is a still further object to provide a process for extracting metal values from manganese oxide ores in which early separation of metals including copper, nickel and/or cobalt from manganese is effected, thereby avoiding complex separation procedures. It is a further object to provide a leach residue from which manganese recovery can be achieved by a simple procedure.
These and other objects will become apparent from the following description taken in conjunction with the accompanying drawings.